It's pretty easy to notice with the magic trackpad—it loses its ability to be "clicked" when it loses power/when you turn it off.
(The trackpad on the laptop does as well, but I feel like you're just less likely to try clicking the trackpad on a macbook/MBP if the computer's not on. Whereas with the external one, you'll notice it when you go to pick it up/move it around and it doesn't accidentally click in your hand.)
(The trackpad on the laptop does as well, but I feel like you're just less likely to try clicking the trackpad on a macbook/MBP if the computer's not on. Whereas with the external one, you'll notice it when you go to pick it up/move it around and it doesn't accidentally click in your hand.)